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Journal of Cleaner Production 52 (2013) 488e494

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Journal of Cleaner Production

journal homepage: www.elsevier .com/locate/ jc lepro

Cleaner process for extraction of sericin using infrared

Deepti Gupta a,*, Anjali Agrawal a, Harshita Chaudhary b, Mohan Gulrajani a, Charu Gupta b

aDepartment of Textile Technology, Indian Institute of Technology, Hauz Khas, New Delhi 110016, IndiabDepartment of Fabric and Apparel Science, Institute of Home Economics, Delhi University, New Delhi 110001, India

a r t i c l e i n f o

Article history:Received 13 September 2012Received in revised form18 February 2013Accepted 9 March 2013Available online 22 March 2013

Keywords:InfraredSilkSericinDegummingWaste management

* Corresponding author. Tel.: þ91 26591417; fax: þE-mail addresses: deeptibgupta@gmail.com,

(D. Gupta).

0959-6526/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.jclepro.2013.03.016

a b s t r a c t

Silk fibre as produced by the silk worm, comes encased in a gum called sericin which is removed toimpart lustre, handle and smoothness to the silk filament. In recent years, sericin has itself been creditedwith important biological properties and is being used by the food, pharma and cosmetics industry.Conventional processes used for the removal of sericin are based on soap and alkali, and discharge largevolumes of sericin and chemicals into the textile wastewaters. Others like the high temperature highpressure (HTHP) process damage silk, are energy intensive and degrade sericin considerably. In thisstudy, a novel approach is proposed to control pollution and minimize waste in wet processing of silk.Process conditions for extraction of sericin from silk waste using infra-red (IR) machine have beendeveloped. Complete extraction of sericin from silk waste could be obtained using a lower temperature,lower time of treatment and lesser water consumption as compared to the conventional high temper-ature high pressure (HTHP) process. Not only does the process reduce the amount of water and chemicalsrequired in conventional processing, it would also reduce the pollution load considerably by not allowingany sericin to go into the effluent. Complete recovery of non-degraded sericin is achieved by a simplespray drying method as compared to multiple filtration and precipitation processes required in soapdegumming. The paper also proposes a complete protocol for qualitative and quantitative assessment ofsericin protein based on UV, FTIR and Fluorescence spectra. Results show for the first time that IR heatingcan be used to develop a greener and more efficient degumming process for silk.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Silk is composed of 2 proteins namely fibroin which is fibrousand sericin which is globular in nature. Fibroin has been used for along time inmanufacturing of apparel and home textiles and is nowbeing investigated as a biomedical product for specialized appli-cations (Zhang, 2002). Sericin has to be removed from fibroin inorder for the fibre to acquire lustre, softness, smoothness, white-ness and dyeability. It is removed by the process of degumming,during which sericin is hydrolyzed or solubilized with the help ofvarious agents andmedia causing about 20e25% weight loss in silk.It is estimated that about 1 million t (fresh weight) of cocoons areproduced worldwide; fromwhich approximately 50,000 t of sericinis discharged into water bodies annually (Aramwit et al., 2012).Sericin waste solution contains high BOD (4,840 mg/L), COD(8870 mg/L) and nitrogen content (11%) creating a huge environ-mental burden (Vaithanomsat and Kitpreechavanich, 2008). Thus,there is a need to develop degumming methods that prevent

91 26581103.deepti@textile.iitd.ernet.in

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environmental problems through pollution prevention and wasteminimization (Moore and Ausley, 2004).

Sericin, which until recently, was considered to be a wasteproduct of the silk processing industry has now been attributedwith several important properties such as excellent moisture ab-sorption and release properties (GenÇ et al., 2009), UV resistance(Patel and Modasiya, 2011) anticoagulant, antioxidant activities(Sarovart et al., 2003) and inhibitory action of tyrosinase (Aramwitet al., 2010). Given the high commercial value of this product, thereis a need to develop degumming methods which do not degradesericin and also allow maximum recovery from the degummingbath (Ki et al., 2009). Recovering sericin from waste water reducesthe environmental impact of silk processing and, at the same timeyields a valuable ingredient for food (Padamwar and Pawar, 2004),pharma and cosmetic industry, leading to considerable social andeconomic benefits (Kundu et al., 2008).

Sericin can be removed from fibroin by boiling (Sothornvit et al.,2010), use of alkali (Rajkhowa et al., 2011), soap (Mahmoodi et al.,2010a,b), detergents (Bianchi and Colonna, 1992) or organic sol-vents like tartaric and citric acid (Khan et al., 2010). Enzymaticmethods based on proteolytic enzymes have also been proposed(Arami et al., 2007). However, the higher cost and other concerns

D. Gupta et al. / Journal of Cleaner Production 52 (2013) 488e494 489

regarding the use of enzymes have so far limited the developmentof the process (Freddi et al., 2003). Another approach is to use hightemperature and high pressure (HTHP) to remove sericin from silk(Li et al., 2012). Extraction of sericin by HTHP method is free ofchemicals, but produces fumes, is messy, time consuming and maydamage fibroin (Aramwit et al., 2012). Table 1 presents a compar-ison of the conventional degumming methods. None of the papersreferred in the table provides any data on the amount or quality ofsericin obtained as recovery of sericin was not attempted in thesestudies.

Industrially, extraction with soap is the most widely usedtechnique because of cost effectiveness and the quality of fibroinobtained. Use of soap and detergent adds further to the pollutionload and it is difficult to recover pure sericin from soap degummingliquor. However, once the importance of sericin as a commercialproduct was realized, attempts were made to recover it from thedegumming bath (Fabiani et al., 1996). Recovery of sericin fromsoap alkali bath has been attempted using micro, ultra and nanofiltration methods (Capar et al., 2008). Drying has been carried outusing spray drying (GenÇ et al., 2009), freeze drying or tray drying(Vaithanomsat and Kitpreechavanich, 2008). Other methods ofpurification include precipitation by ethanol for lab scale applica-tions (Kurioka et al., 2004). Search is therefore on to find alternatemethods for removing sericin using chemical substitution whereminimum or no quantities of chemicals are used (Ozturk et al.,2009). Newer energy sources are also being tried to improve theefficiency of conventional textile processes. In a recent study,Mahmoodi et al., 2010a,b used ultrasonic energy combined withenzymes as an efficient and eco-friendly process for sericinremoval. It is seen that the structural and functional properties ofsericin depend on the method used for its extraction and recovery(Gulrajani et al., 2009). Fig.1 shows the schematic for steps requiredin the conventional silk degumming process and recovery of sericinfrom waste waters.

Infrared (IR) heating is becoming popular in process industriesas an effective and non-polluting method of activation because ofreportedly higher thermal efficiency and faster heating rate ascompared to convective heating (Sakai and Hanzawa, 1994). It isrecognized as a method with easy control of heating temperature,convenient application, and significant savings of space and energyconsumption (Wang et al., 2012). IRmachines work on the principleof direct heating where heat is transferred directly to the center ofmaterial in the form of electromagnetic waves, without heating thesurrounding air (Krishnamurthy et al., 2008). No studies have beenreported on use of IR for removal of sericin from silk.

In this study, an IR heating machine was used to extract sericinfrom silk waste in an aqueous bath. Results were benchmarkedagainst the conventional method of extraction using HTHP. Qualityand yield of protein obtained by various methods was comparedwith that of standard sericin. A systematic protocol for characterizingsericin in a qualitative and quantitative manner has been proposed.Fig. 2 shows the plan of experiments conducted in the study.

Table 1Conventional methods used in degumming of silk.

S. No. Method of degumming Advantages

1 Boiling Simple process

2 Soap and alkali Simple process Most wid

3 Organic solvents (tartaric acid, citric acid) Milder in action compare

4 High Temperature High Pressure (HTHP) Does not result in any im

5 Enzymes Saves water, energy, che

2. Materials and methods

2.1. Materials

Raw silk waste was procured from Central Silk Research Insti-tute of Technology, Central Silk Board, Bangalore, India. Thechemical reference substance, Sericin (S 5201), extracted fromBombyx mori, was procured from Sigma Aldrich, USA. Deionizedwater was used for all extractions. Analytical grade chemicals, so-dium carbonate (Qualigens, India), sodium hydroxide (Qualigens,India), copper sulphate (Merck, USA), sodium potassium tartarate(Merck, USA), Bovine serum albumin (Spectrochem, India) andFolin Ciocalteau’s phenol reagent (Merck, USA) were used for theexperiments.

2.2. Extraction of sericin

The effect of process parameters shown in Table 2 was studiedon extraction efficiency of sericin from silk waste using HTHP andIR heating.

The extraction efficacy is expressed in terms of the maximumextraction yield calculated as per equation (1):

Yieldð%Þ ¼ WS

WSW(1)

where

WS (g) ¼ initial weight e final weightWSW (g) ¼ initial weight of the raw silk waste

Extraction was carried out in a High Temperature High Pressure(HTHP) beaker dyeing machine (R.B. Electronic and Engg. Pvt. Ltd,India) and an IR dyeing machine DLS 7000 (Daelim Scarlet, Korea)equipped with six medium-wave IR heating tubes.

2.2.1. Preparation of sericin powderThe aqueous liquor obtained after extraction was dried by two

methods- tray and spray drying.For tray drying, the extracted liquor was kept in a glass tray, in a

Venticell hot air oven (MMM Group, Canada) at 40 �C till a drypowder was obtained.

Spray drying was done using a laboratory spray dryer LU-227Advanced (Labultima, India), at inlet temperature of 110 �C andthe atomization pressure of 3e4 kg/cm2.

2.3. Kinetic studies

For measuring the effect of time on the rate of sericin extractionin IR machine, kinetic studies were carried out at 80 �C and 100 �C,at M L R of 1:20.

Limitations References

Time consuming, degrades sericin,damages fibroin.

Sothornvit et al., 2010

ely used Effluent problems, Difficulty inrecovering sericin

Rajkhowa et al., 2011

d to alkali Effluent problems, non-efficient Khan et al., 2010;Arami et al., 2007

purity Causes fumes, odour, messydamages fibroin

Gulrajani et al., 2009;Yong Cho et al., 2003

micals Expensive, Degrade sericinextensively

Arami et al., 2007;Gulrajani et al., 2000

Silk waste

Degumming

BoilingAlkaliSoap /detergentEnzymesHTHP

Cocoons Silk fabric

Fibroin

CentrifugingGarments, Home textiles,Biomedical products

Pharmaceuticals, CosmeticsFood, Textiles

Waste water

Drying

Precipitation

Filtration

Sericin powder

Fig. 1. Conventional process used for degumming of silk and recovery of sericin.

D. Gupta et al. / Journal of Cleaner Production 52 (2013) 488e494490

2.4. Characterization of sericin powder

2.4.1. Assessment of protein contentThe protein content in sericin powder was assayed by Lowry’s

method using bovine serum albumin (BSA) as a standard.

2.4.2. X-ray diffraction (XRD) analysisXRD was conducted at ambient temperature with X’pert PRO X-

ray diffractometer (PANalytical, Netherlands) having an X-ray tubeproducing monochromatic CuKa radiation. Powdered sampleswere mounted onto sample stage to record the crystallinity index.Sample stage was mounted on horizontal axis and the diffractedbeam optics and the detector were mounted on 2q axis. The scan-ning rate was 0.5�/min at 2q ¼ 5�e35� under the accelerationvoltage of 30 kV and 20 mA.

2.5. Spectroscopic analysis

2.5.1. Ultraviolet spectraUltraviolet spectrum of sericin samples was recorded on a D-

2750 UVeVis spectrophotometer (Shimadzu, Singapore). Standardcurve was drawn for standard sericin sample obtained from Sigma.

2.5.2. Fourier transform infrared (FTIR) spectroscopyThe FTIR spectra of sericin samples were recorded on BX FTIR

spectrophotometer (PerkinElmer, US) in order to determine thepresence of functional groups in sericin. KBr pellet method wasused and the spectra were recorded in the region of 4000e400 cm-1.

2.5.3. Fluorescence spectraFluorescence spectra of the sericin samples were recorded on

SpectraMax M2e (Molecular Devices, US). The excitation wavelength

was 295 nm and emission wavelength range was 300 nme450 nm.

3. Results and discussion

Silk waste was degummed using HTHP and IR methods in anaqueous bath. Yield of sericin obtained under varying process pa-rameters using both methods was calculated. Effect of extractionparameters on quality of protein obtained by various methods ofextraction and drying was compared. Characterization data forsericin samples was generated and is presented in the followingparagraphs.

Aq. extraction

Liquor

Drying

Sericin powder

Characterization

Yield

Protein

Ultraviolet spectroscopy

FTIR spectroscopy

Fluorescence spectroscopy

High Temp. High Pressure (HTHP)

Infrared (IR)

Spray Drying Tray Drying

X-ray diffraction

Silk waste

Fig. 2. Plan of experiments conducted in the study.

0

5

10

15

20

25

30

0 30 60 90 120 150

Yie

ld (

%)

Time (min)

IR (100°C)

IR (110°C)

IR (120°C)

HTHP (100°C)

HTHP (110°C)

HTHP (120°C)

Fig. 3. Effect of temperature and time on yield of sericin (LR-1:20).

10

15

20

25

30

Yie

ld (

%)

80°C

100°C

D. Gupta et al. / Journal of Cleaner Production 52 (2013) 488e494 491

3.1. Effect of temperature and time of extraction on yield

Fig. 3 shows the yield of sericin obtained at different time andtemperature of extraction, using IR and HTHP method. Maximumyield of sericin (26% w/w) was obtained after 120 min of extractionat 110 �C in IR method. This indicates that all sericin has beenremoved under these conditions as the maximum amount ofsericin present in silk waste is around 26%. Therefore further in-crease in temperature to 120 �C does not give a higher yield. Trendobserved in HTHP extraction is quite different from that obtained inIR extraction. Effect of temperature is much more prominent inHTHP as yield improves from 14.5% at 100 �C to a maximum of23.5% at 120 �C, 120 min of extraction.

Comparative studies on the effect of time and temperature ofextraction of sericin from silk waste, using IR and HTHP method,indicate that process parameters have a significant effect on theyield. In HTHP method, only about 50% (14.5%) of total sericinpresent in the waste is extracted at 120 min of treatment time.Under the same process conditions, IR method gives completeextraction of about 26%. At higher temperature of 110 �C and 120 �C,in HTHP, the yield increases to 23%. Though yield increases withtime as well as temperature of extraction in HTHP, total yield ofsericin is much lower in all cases than that obtained in IR methodand saturation value of 26% is never attained.

The difference in yield of sericin from IR and HTHP method, islikely due to the difference in principle of heating employed in thetwo cases. HTHP heating is based on convection heating in whichthermal energy is indirectly transferred from the glycerine bath to

Table 2Process parameters studied.

Parameters Values

Time (min) 60, 90, 120Temperature (�C) 100, 110, 120Material: liquor ratio 1:20, 1:30, 1:40, 1:50, 1:100, 1:150

the containers. Infrared heating, on the other hand is a form ofradiation heating in which heat is transferred directly to the ma-terial in the form of electromagnetic waves. IR energy, due to directheating, elicits vibrational modes in water through a change indipole moment, thus causing water to act as an abrading agent (Linet al., 2009). This could explain why more sericin is extracted in IRat lower temperature, time and LR as compared to HTHP heating.

3.2. Rate of extraction of sericin in IR method

Since nearly all sericin was extracted at 60 min of treatmenttime at 100 �C in IR, further studies were carried out to see if it waspossible to lower the time or temperature of extraction to lower theenergy consumed. Amount of sericin extracted from silk waste at80 �C and 100 �C at different time of treatment up to 180 min wasstudied. Results are shown in Fig. 4. It can be seen that sericinextraction in IR method is quite sensitive to temperature. The rateof extraction as well total amount of sericin extracted was muchhigher at 100 �C, very little sericin being obtained at 80 �C. Nearlyall of sericin (24%) is extracted at 60 min of time at 100 �C whileonly 12% sericin is removed at 60min at 80 �C. Even after treatmentfor 180 min only 13% sericin which is half of the total amountpresent, is extracted indicating that 100 �C is the optimum tem-perature for extracting sericin from silk waste.

3.3. Effect of material to liquor ratio (LR) on yield

In order to minimise the water consumption, optimizing the LRis critical in development of a process for wet treatment of textiles.Results of extraction of silk waste carried out at various LR usingHTHP and IR method are shown in Fig. 5. Amount of sericin

0

5

0 50 100 150 200

Time (min)

Fig. 4. Effect of temperature on rate of extraction of sericin in IR machine.

0

0.4

0.8

1.2

1.6

2

Standardsericin

IR(spray)

IR (tray) HTHP(spray)

HTHP(tray)

1.73

1.24

0.59 0.520.28

Pro

tein

Con

cent

rati

on (m

g/m

l)

Samples

Fig. 6. Protein content of sericin powders.

D. Gupta et al. / Journal of Cleaner Production 52 (2013) 488e494492

extracted from silk waste is particularly sensitive to the change inliquor ratio in IR extraction method. The yield falls progressivelyfrom 22.83% to 6% as LR increases from 1:20 to 1:150. In case ofHTHP extraction, yield increases from 8.41% to 11.6% as liquor ratioincreases from 20 to 50. No increase is observed on increasing LRfrom 50 to 150. Based on these observations, for all subsequenttests, extraction was carried out at LR of 1:20 in infrared as well asHTHP machine.

Effect of LR on sericin yield is very different in the two methods.It is interesting to note that in IR extraction, yield is maximum (24%)at LR of 1:30 while in HTHP an LR of 1:50 is required to maximizethe yield (10.5%) of sericin. This indicates that much more sericincan be extracted from silk waste using less water when IR methodis used. Thus use of IR method not only reduces the consumption ofwater during extraction, but also translates into power savingsduring the drying process, as less amount of water will have to beevaporated to obtain sericin powder.

3.4. Characterization of sericin samples

The special properties of sericin such as moisture absorption,antioxidant and cell rejuvenation depend on the quality of proteinobtained. Studies were therefore carried out to determine the effectof method of extraction and drying used to produce sericin powder,on the properties of the end product. Samples extracted by IR andHTHP method and dried using a laboratory oven and a spray dryerwere characterized in terms of protein content, UV, IR and Fluo-rescence spectra and XRD analysis. Quality of protein obtained ineach case was compared with that of standard sericin sample.

3.4.1. Protein contentComparative data for protein content of sericin samples pre-

pared in the lab with that of the standard sericin powder is pre-sented in Fig. 6. Standard sample was found to have proteinconcentration of 1.73 mg/ml, while powder recovered from spraydrying of IR extracted liquor had 1.24 mg/ml and sericin obtainedby HTHP spray drying technique had 0.52 mg/ml of protein. Thetray dried samples had even less protein.

In all cases, protein content was found to be less than that ofstandard sample. Since the source in this case is silk waste, it ispossible that some degradation has occurred during prior pro-cessing. Among the test samples, protein concentrationwas highestin samples extracted by IR and dried by spray drying and lowest insamples extracted by HTHP and dried in hot air. HTHP and traydrying are both heat intensive methods and thereby showedmaximum loss of protein.

0

5

10

15

20

25

0 30 60 90 120 150

Yie

ld (

%)

Liquor Ratio

IR

HTHP

Fig. 5. Effect of liquor ratio on yield of sericin (100 �C, 60 min).

3.4.2. X-ray diffraction analysisFig. 7 shows theXRDcurves for laboratoryprepared and standard

sericin samples. All curves exhibit a strong diffraction peak around2q ¼ 20.5�, suggesting that the sericin has a b e sheet structure andthat the structure has not changed during processing. It is observedthat these peaks are broad, indicating that the powders are amor-phous. XR diffractograms were found to be similar for all sericinsamples including the reference sample. Similar results have beenreported in earlier studies (Lamoolphak et al., 2008).

3.4.3. Ultraviolet spectraUV spectra of standard and laboratory prepared sericin samples

are presented in Fig. 8. Characteristic peak, attributed to the ab-sorption of amino acids was observed at 275.40 nm in the standardsericin sample (A). For other samples, the peak was observed at285 nm for (B), 280 nm for (E), 273 nm for (C) and 280 nm for (D).

UV spectrum can be used to evaluate the quality of proteinssince they are known to absorb strongly in ultraviolet regionmainlydue to peptide bonds and aromatic acids. The aromatic amino acidslike tryptophan, tyrosine and cysteine are known to absorb in therange of 260e290 nm due to p / p* transition. Standard sampleshowed the characteristic protein peak at 275.4 nm but in allextracted samples a shift in this peak was observed indicating achange in the properties of protein. Sample C obtained by IR andspray drying showed a spectrum closest to that of the standard.

3.4.4. FTIR analysisThe IR spectra of various sericin samples are presented in Fig. 9.

Amide peaks are involved in a polypeptide backbone, and therefore

Fig. 7. X-ray diffractograms of sericin samples (A: Standard, B: HTHP spray, C: IR spray,D: HTHP tray, E: IR tray).

Fig. 8. UV absorption spectra of sericin powders (A: Standard sericin, B: IR tray, C: IRspray, D: HTHP spray, E: HTHP tray).

Fig. 10. Fluorescence spectra of sericin samples (A: Standard sericin, B: IR tray, C: IRspray, D: HTHP ray, E: HTHP tray).

D. Gupta et al. / Journal of Cleaner Production 52 (2013) 488e494 493

are sensitive to the secondary structure and molecular orientationof protein. The peaks in the region of 3000e3500 cm-1 are amide Aand amide B bonds associated with NeH stretching vibrations.

Sericin extracted from HTHP and IR heating showed absorptionbetween 1600 and 1700 cm-1 confirming amide I absorption whicharises predominantly from the C]O stretching vibration and is themost useful peak for determining secondary structure of proteins.The peak at 1540 cm-1 belongs to amide II which indicates thepresence of a random coil structure. Amide II peak seems to havedissolved in the tray dried sericin samples suggesting that someconformational change has occurred in the samples. Signature peakfor sericin at 1400 cm-1 was observed in case of all the samples. Inaddition, the amide III characteristic peak which arises mainly fromthe CeN stretching vibration coupled to the NeH plane bendingvibration was found to shift to 1240 e 1250 cm-1 indicating achange from random coil conformation to b sheet structure. No

Fig. 9. FTIR spectra of sericin powders (A: Standard sericin

major difference was observed in IR spectra of standard and testsamples prepared from different methods. Results are similar tothose reported by Teramoto and Miyazawa (2005) and Zhang andWyeth (2010).

3.4.5. Fluorescence spectroscopyFluorescence spectra of standard and test samples was recorded

to determine if the extraction parameters affect the conformationalstate of sericin protein in any way. Spectra are shown in Fig. 10. Itcan be seen that standard sericin (A) gives a distinct peak at355 nm. All other samples show a minor shoulder around 355 nmand a distinct peak at 310 nm. Sample (C) IR/spray is the only othersample showing a peak at 355 nm.

The fluorescence of a folded protein is a mixture of the fluo-rescence from individual aromatic residues. Most of the intrinsicfluorescence emissions of a folded protein are due to excitation oftryptophan residues, with some emissions due to tyrosine andphenylalanine. Typically, tryptophan has the excitation wavelengthof 295 nm and an emission peak that is solvatochromic, rangingfrom ca. 300e350 nm depending on the polarity of the localenvironment (Lackowicz, 2002). In Fig. 10, all extracted samples

, B: IR tray, C: IR spray, D: HTHP spray, E: HTHP tray).

D. Gupta et al. / Journal of Cleaner Production 52 (2013) 488e494494

show a fluorescence pattern which is different from that of thestandard sample A which shows a single distinct fluorescence peakat 355 nm. It can thus be inferred that some changes do take placeduring extraction that affect the conformational state of sericinprotein. The effect of these changes on performance of sericin needsto be established.

4. Conclusions

Process parameters used in the extraction as well as drying ofsericin are critical in deciding the yield of sericin as well as thenature of protein obtained. Method of heating, time and tempera-ture of extraction, as well as the liquor ratio, all affect the amount ofsericin extracted. Extended exposure to heat during HTHP extrac-tion and tray drying method appears to denature and degrade theprotein. Change in the fluorescence spectra of samples exposed tothese conditions vis a vis standard sample, indicates a changedconformational state often associated with protein degradation.The change is minimal when IR heating is employed for extractionand spray drying is used for making the powder, indicating thatthese methods are better for maintaining the quality of sericinprotein.

This paper, lays down a complete step by step protocol forassessing and characterizing the quality of sericin protein. It hasbeen shown that IR and XRD studies are not sensitive enough to beused to evaluate the quality of sericin protein obtained fromvarioussources. UV spectra are quite characteristic and can be used forfingerprinting. Fluorescence spectra are most sensitive to changesin conformational state of protein and can be used to assess thesame.

Although studies have been reported on extraction of sericinusing various methods, IR energy has never been used before forthe purpose. In this study, complete extraction of sericin wasaccomplished using IR heating, without using any chemicals. Thenovelty of the proposed process lies in the fact that it is a ChemicalSubstitution Technology that does away with use of chemicals likealkali, soap and synthetic detergents whilst at the same timeachieving a better functionality by minimizing the damage tosericin. The process makes use of minimum amount of water and iscompletely free from chemicals thus making it a green processleading to significant reduction in pollution load of a silk processingunit. Compared to conventional soap degumming process whereseveral steps like filtration, separation and centrifuging arerequired to separate sericin from soap, this process is much cleaneras recovery of sericin can be done by spray drying the liquordirectly. The limitation of this process is that large scale extractorsbased on IR heating are as yet not available commercially. Technoeconomic studies need to be carried out to assess the commercialviability of this novel method.

Acknowledgements

Authors are grateful to the Department of Biotechnology, Gov-ernment of India for providing financial support for this researchwork. Help provided byMs Abhilasha Rangi in formatting of figuresis thankfully acknowledged.

References

Arami,M., Rahimi, S., Mivehie, L., Mazaheri, F., Mahmoodi, N.M., 2007. Degumming ofPersian silk with mixed proteolytic enzymes. J. Appl. Polym. Sci. 106, 267e275.

Aramwit, P., Damrongsakkul, S., Kanokpanont, S., Srichana, T., 2010. Properties andantityrosinase activity of sericin from various degumming extraction methods.Biotechnol. Appl. Biochem. 55, 91e98.

Aramwit, P., Siritientong, T., Srichana, T., 2012. Potential applications of silk sericin, anatural protein from textile industry by-products. Waste Manage. Res. 30 (3),217e224.

Bianchi, A.S., Colonna, G.M., 1992. Developments in degumming of silk. MelliandTextil 73, 68e75.

Capar, G., Aygun, S.S., Gecit, M.R., 2008. Treatment of silk production wastewatersby membrane processes for sericin recovery. J. Membr. Sci. 325, 920e931.

Fabiani, C., Pizzichini, M., Spadoni, M., Zeddita, G., 1996. Treatment of waste waterfrom silk degumming processes for protein recovery and water reuse. Desali-nation 105, 1e9.

Freddi, G., Mossotti, R., Innocenti, R., 2003. Degumming of silk fabric with severalproteases. J. Biotechnol. 106, 101e112.

GenÇ, G., Bayraktar, O., BaSal, G., 2009. A research on the production of silk sericinpowders by using spray drying method. Tekstil ve Konfeksiyon 19 (4), 273e279.

Gulrajani, M.L., Agarwal, R., Chand, S., 2000. Degumming of silk with fungal pro-tease. Indian J. Fiber Text. Res. 25, 138e142.

Gulrajani, M.L., Purwar, R., Prasad, R.K., Joshi, M., 2009. Studies on structural andfunctional properties of sericin recovered from silk degumming liquor bymembrane technology. J. Appl. Polym. Sci. 113, 2796e2804.

Khan, M.R., Tsukada, M., Gotoh, Y., Morikawa, H., Freddi, G., Shiozaki, H., 2010.Physical properties and dyeability of silk fibres degummed with citric acid.Bioresour. Technol. 101, 8439e8445.

Ki, C.S., Park, Y.H., Jin, H.J., 2009. Silk protein as a fascinating biomedical polymer:structural fundamentals and applications. Mol. Res. 17 (12), 935e942.

Krishnamurthy, K., Khurana, H.K., Jun, S., Irudayaraj, J., Demirci, A., 2008. Infraredheating in food processing: an overview. Compr. Rev. Food Sci. Food Saf. 7, 1e12.

Kundu, S.C., Dash, B.C., Dash, R., Kaplan, D.K., 2008. Natural protective glue protein,sericin bioengineered by silkworms: potential for biomedical and biotechno-logical applications. Progess. Polym. Sci. 33, 998e1012.

Kurioka, A., Kurioka, F., Yamazaki, M., 2004. Characterization of sericin powderprepared from citric acid degraded sericin polypeptides of the silkworm,Bombyx mori. Biosci. Biotechnol. Biochem. 68 (4), 774e780.

Lackowicz, J.R., 2002. Protein Flourescence. In: Topics in Fluorescence Spectroscopy,Vol. 6. Kluwer Academic Publishers, New York.

Lamoolphak, W., Eknamkul, W.D., Shotipruk, A., 2008. Hydrothermal productionand characterization of protein and amino acids from silk waste. Bioresour.Technol. 99, 7678e7685.

Li, G., Liu, H., Li, T., Wang, J., 2012. Surface modification and functionalization of silkfibroin fibres/fabric toward high performance applications. Mater. Sci. Eng. C.http://dx.doi.org/10.1016/j.msec.2011.12.013.

Lin C.M., Huang, Y.T., Yao, Y.T., Lin, C. H. 2009. Manufacturing process and propertiesevaluation of anti electromagnetic/far infrared ray for complex nonwoven,Proceedings of the 10th Asian Textile Conference, ATC-10, September 7e9,Ueda, Japan.

Mahmoodi, N.M., Arami, M., Mazaheri, F., Rahimi, S., 2010a. Degradation of sericin(degumming) of Persian silk by ultrasound and enzymes as cleaner and envi-ronmentally friendly process. J. Clean. Prod. 18, 146e151.

Mahmoodi, N.M., Moghimi, F., Arami, M., Mazaheri, F., 2010b. Silk degumming usingmicrowave irradiation as an environmentally friendly surface modificationmethod. Fibres Polym. 11, 234e240.

Moore, S.B., Ausley, L.W., 2004. Systems thinking and green chemistry in the textileindustry: concepts, technologies and benefits. J. Clean. Prod. 12, 585e601.

Ozturk, E., Yetis, U., Dilek, F.B., Demirer, G.N., 2009. A chemical substitution study fora wet processing textile mill in Turkey. J. Clean. Prod. 17 (2), 239e247.

Padamwar, M.N., Pawar, A.P., 2004. Silk sericin and its applications: a review. J. Sci.Ind. Res. 63, 323e329.

Patel, R.J., Modasiya, M.K., 2011. Sericin-pharmaceutical applications. Int. J. Res.Pharm. Biomed. Sci. 2, 913e917.

Rajkhowa, R., Wang, L.J., Kanwar, J.R., Wang, X.G., 2011. Molecular weight andsecondary structure change in Eri silk during alkali degumming and powdering.J. Appl. Polym. Sci. 119, 1339e1347.

Sakai, N., Hanzawa, T., 1994. Applications and advances in far infrared heating inJapan. Trends Food Sci. Technol. 5, 357e362.

Sarovart, S., Sudatis, B., Meesilpa, P., Grady, B.P., Magaraphan, R., 2003. The use ofsericin as anantioxidant and antimicrobial for polluted air treatment. Rev. Adv.Mater. Sci. 5, 193e198.

Sothornvit, R., Chollakup, R., Suwanruji, P., 2010. Extracted sericin from silk wastefor film formation. Songklanakarin J. Sci. Technol. 32 (1), 17e22.

Teramoto, H., Miyazawa, M., 2005. Molecular orientation behaviour of silk sericinfilm as revealed by ATR infrared spectroscopy. Biomacromolecules 6, 2049e2057.

Vaithanomsat, P., Kitpreechavanich, V., 2008. Sericin separation from silk degum-ming wastewater. Sep. Purif. Technol. 59, 129e133.

Wang, R., Jiang, W., Li, S., Yang, H., Dong, Y., Fu, Y., 2012. Application research oninfrared drying in silk re-reeling process. Textile Res. J. 82 (13), 1329e1336.

Yong Cho, K., Moon, J.Y., Lee, Y.W., Lee, K.G., Yeo, J.H., Kweon, H.Y., Kim, K.H.,Cho, C.S., 2003. Preparation of self assembled silk nanoparticles. Int. J. Biol.Macromol. 32, 36e42.

Zhang, Y.Q., 2002. Applications of natural silk protein sericin in biomaterials. Bio-technol. Adv. 20, 91e100.

Zhang, X.M., Wyeth, P., 2010. Using FTIR spectroscopy to detect sericin on historicsilk. Sci. China 53, 626e631.